I might be able to answer a few of your questions, even though I'm no marine expert. I read a lot of reef keeping forums such as Reef Central and Nano-Reef.com. Take everything I say with a pinch of salt though as I have had no experience with caring for a reef aquarium
I fail to understand why most people have it in their heads that if you want a sump you have to drill the tank :dunno: IMO if your tank isn't already drilled then it isn't worth the hassle to do so
You can buy (or DIY) an overflow box like this :thup:
These are the nasty ones that you want to avoid though.
I have read that canister filters can be a bit of a hassle when it comes to cleaning time. If you spill any water when you are cleaning it, remember it has salt in it From what I've read on other forums, most people who have replaced their canister filters with sumps seem pretty happy. Also the advantage of having a sump is that the water in the display tank needs to reach a certain level before it flows into the overflow box/chamber. This means that you will always have a constant water level in the display tank, and the water level in the sump will fluctuate. You will need to use some sort of auto top off device to combat evaporation, and it is much nicer if you can hide this in the sump as opposed to having it visible in your display tank. Sumps also allow you to fit a lot more equipment into your system and provide higher water quality from what I've read.
It depends on what corals you want. A 4x24w T5HO unit should be sufficient for most soft corals and large polyp stony corals, and some types of small polyp stonies. IMO LEDs aren't yet advanced enough to provide a complete lighting solution. Although there is not doubt that LEDs do an awesome job at growing corals, I have read that a lot of people who have purchased LEDs have switched back to halides and T5s because the latter provide a broader spectral output and are more aesthetically pleasing to view corals under. LEDs are still great for supplementary lighting and moonlights though
Perculas and ocellaris will be fine. A lot of the other species of clowns can get quite big and aggressive from what I've read.
Here's some suggestions fish that should be happy in a 130L tank with clowns.
Amblyeleotris wheeleri
Centropyge bispinosus
Chromis retrofasciata
Chrysiptera parasema
Cryptocentrus cinctus
Elacatinus oceanops
Gobiodon citrinus
Gobiodon okinawae
Nemateleotris decora
Nemateleotris magnifica
Opistognathus rosenblatti
Stonogobiops nematodes
Synchiropus ocellatus
Synchiropus picturatus
Synchiropus splendidus
Pseudochromis fridmani
Pterapogon kauderni
I hope I could be of some help to you. I am looking forward to seeing this tank up and running :bounce: